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Tuesday, September 20, 2011

Assessment from BAN-PT to Teknik Elektro ST-INTEN

At September 19, 2011, my University Department (Electronic & Electrical Engineering / Teknik Elektro ST-INTEN) organized a visit of BAN-PT (Badan Akreditasi Nasional Perguruan Tinggi) to assess Our Department. BAN-PT is National Higher Education Accreditation Board which function to assess and give accreditation to higher educations in Indonesia according to defined service standard. BAN-PT representers were Prof. Dr. Ir. Maria Angela Kartawidjaja, MKom., and Dr. Ir. Anak Agung Putri Ratna, MEng.. Thank You very much for Your Kind Visit.

With humble, below are photos of the visit:

Saturday, April 23, 2011

Communication Microphone for High Power Transmitter

This is my design, and suitable for most of Amateur Radio & whatever transmitters which have power up to 100W PEP. The keys of this design compared to my previous designs are utilization of 2 RF filters located after condenser mic and voltage supply from power supply, and good ground connection connected from ground section of this mic preamp to ground installation at your soil. These are ways to suppress RF feedbacks from entering processing in transistor (2SC828).

This design has been tested using 100W transceiver with antenna SWR 1-1.5, and still produced clear voice. Mic used is cheap 2 leads condenser mic. Under is photo of this design after placed at PCB:

If you like to design microphone, especially mic that is used with high power transmitter, You have to be able to suppress RF that comes back to mic from antenna. One simple thing is to make your antenna SWR as small as possible (try SWR 1.0). With SWR 1.0, all of power generated by final amplifier would be dissipated at antenna, with higher SWR, there would be portion of power reflected back from antenna to final amplifier causes RF feedbacks on mic system. If your SWR already 1.0, but still You are having RF feedbacks, then You should utilize RF filter.

At this design, RF filter composed of one 27mH inductor (looks like black capacitor at photo), and two 1500pF ceramic capacitors. For higher transmitter power, You could experiment with more suppressing RF filter, logically: higher inductor value, and higher capacitors value. Utilization of grounded metal box, logically would suppress RF more. Try as far as You could until RF is not processed at mic circuit.

Components should be placed as close as possible, and cables should be as short as possible. These would reduce RF feedbacks. This is because long cables function as antennas.

+12-13.8 VDC could be taken directly from ordinary power supply.

22n & 10n are coupling capacitors. Their main function is to keep DC around transistor, while AC could travel from outside to transistor, and from transistor to outside. This unique capacitor characteristic could be used to determine audio tone of this mic system. Lower capacitor value tends to produce higher audio frequency (treble), and vice versa. Basic criteria when You are designing audio system for communication is Signal to Noise Ratio (SNR). Higher SNR, better, of course with clear signal without distortion. You could try to investigate Noise (QRM & QRN) on working frequency, and try to experiment with various audio tones, to try to make highest SNR, eg. if noise figure is bass, and Your audio tone is bass as well, so SNR would be low, so You have to make Your audio tone treble, so SNR would be higher, and Your audio would be more readable.

22n & 10n are green mylar capacitors.

To reduce fatigue, this mic could be designed as desk microphone.

Have a nice try and Good DX.